1 // Boost.Range library 2 // 3 // Copyright Arno Schoedl & Neil Groves 2009. 4 // Use, modification and distribution is subject to the Boost Software 5 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at 6 // http://www.boost.org/LICENSE_1_0.txt) 7 // 8 // For more information, see http://www.boost.org/libs/range/ 9 // 10 #ifndef BOOST_RANGE_DETAIL_EXTRACT_OPTIONAL_TYPE_HPP_INCLUDED 11 #define BOOST_RANGE_DETAIL_EXTRACT_OPTIONAL_TYPE_HPP_INCLUDED 12 13 #if defined(_MSC_VER) && (_MSC_VER >= 1200) 14 # pragma once 15 #endif 16 17 #include <boost/config.hpp> 18 19 #ifdef BOOST_NO_PARTIAL_TEMPLATE_SPECIALIZATION 20 21 #define BOOST_RANGE_EXTRACT_OPTIONAL_TYPE( a_typedef ) \ 22 template< typename C > \ 23 struct extract_ ## a_typedef \ 24 { \ 25 typedef BOOST_DEDUCED_TYPENAME C::a_typedef type; \ 26 }; 27 28 #else 29 30 namespace boost { 31 namespace range_detail { 32 template< typename T > struct exists { typedef void type; }; 33 } 34 } 35 36 // Defines extract_some_typedef<T> which exposes T::some_typedef as 37 // extract_some_typedef<T>::type if T::some_typedef exists. Otherwise 38 // extract_some_typedef<T> is empty. 39 #define BOOST_RANGE_EXTRACT_OPTIONAL_TYPE( a_typedef ) \ 40 template< typename C, typename Enable=void > \ 41 struct extract_ ## a_typedef \ 42 {}; \ 43 template< typename C > \ 44 struct extract_ ## a_typedef< C \ 45 , BOOST_DEDUCED_TYPENAME boost::range_detail::exists< BOOST_DEDUCED_TYPENAME C::a_typedef >::type \ 46 > { \ 47 typedef BOOST_DEDUCED_TYPENAME C::a_typedef type; \ 48 }; 49 50 #endif 51 52 #endif // include guard 53
